Liquid crystal polyester fiber and producing method thereof

ABSTRACT

Provided is a liquid crystal polyester fiber having high strength, high elastic modulus, high abrasion resistance, excellent processability, and little thermal deformation at high temperature, and also provided is a production method thereof. A liquid crystal polyester fiber, characterized in that the peak half-value width of the endothermic peak (Tm1) observed when measuring by differential calorimetry under rising temperature conditions starting at 50° C. and increasing 20° C./min is 15° C. or higher, the polystyrene-converted weight-average molecular weight is between 250,000 and 2,000,000 inclusive, the peak temperature of the loss tangent (tan δ) is between 100° C. and 200° C. inclusive, and the peak value of the loss tangent (tan δ) is between 0.060 and 0.090 inclusive. A mesh fabric comprising the liquid crystal polyester fiber. A production method for melt liquid crystal polyester fiber, characterized in that liquid crystal polyester fiber obtained by melt-spinning is subject to solid-phase polymerization, and subsequently heat treated at a stretch ratio of at least 0.1% and under 3.0% at a temperature at least 50° C. higher than the endothermic peak temperature (Tm1) as observed when measuring by differential calorimetry under rising temperature conditions starting at 50° C. and increasing 20° C./min.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 37 C.F.R. § 1.53(b) Divisional of copendingU.S. application Ser. No. 15/113,902 filed Jul. 25, 2016, which is theNational Phase under 35 U.S.C. § 371 of International Application No.PCT/JP2015/051451 filed Jan. 21, 2015, which claims priority to JapanesePatent Application No. 2014-016586 filed Jan. 31, 2014, all of which arehereby expressly incorporated by reference into the present application.

TECHNICAL FIELD OF THE INVENTION

Our invention relates to a liquid crystal polyester fiber having highstrength, high elastic modulus, high abrasion resistance, excellentprocessability and less heat deformation at a high temperature, and amanufacturing method thereof.

BACKGROUND ART OF THE INVENTION

A liquid crystal polyester is a polymer consisting of rigid molecularchains, showing high strength and high elastic modulus among fibersproduced in a melt spinning process by applying a heat treatment(solid-phase polymerization) to the molecular chains highly-oriented ina fiber axial direction. As shown in pages 235-256 of Non-patentdocument 1, the liquid crystal polyester has improved heat resistanceand dimensional stability since the solid-phase polymerization increasesits molecular weight to raise its melting point. Thus the liquid crystalpolyester fiber has high strength, high elastic modulus, excellent heatresistance and excellent thermal dimensional stability by applying thesolid-phase polymerization.

On the other hand, the liquid crystal polyester fiber may havedisadvantages such as low interaction in a fiber axial direction andpoor abrasion resistance so that fibrillation is caused by frictions inhigher processing and weaving process, because rigid molecular chainsare highly oriented in the fiber axial direction to form dense crystals.Recently, specifically for filters and screen-printing gauzes made ofmonofilaments, higher weaving density (higher mesh) and larger openingsection areas are demanded in order to improve the performance. Sinceimprovements such as higher single fiber fineness, higher strength andhigher elastic modulus are strongly demanded to achieve this, the liquidcrystal polyester fiber is being counted on because of its high strengthand high elastic modulus. Since the fault decrease in fibril or the likeis also strongly demanded for higher performance at the same time,improvements of abrasion resistance of the liquid crystal polyesterfiber and processability are expected.

Further, thermal deformation should be less even at a high temperaturefor mesh fabric products. For example, a great thermal deformation at ahigh temperature with high load for reducing wrinkles might causenon-uniform openings and degrade performances of screen printing andfiltration. From these viewpoints, it is demanded for the liquid crystalpolyester fiber to improve abrasion resistance and suppress thermaldeformation at a high temperature at the same time.

In order to improve abrasion resistance of liquid crystal polyesterfiber, pages 18-19 of Patent document 1 suggest that liquid crystalpolyester fiber should be heat-treated at the melting point+10° C. ormore, or the endothermic peak temperature (Tm1)+10° C. or more, whereinthe Tm1 is determined by differential calorimetry under temperatureelevation of 20° C./min from 50° C. Although that technology can improvethe abrasion resistance well, it cannot sufficiently suppress thethermal deformation at a high temperature. The great improvement ofabrasion resistance is likely to increase the thermal deformation at ahigh temperature although fiber after the solid-phase polymerization isheat treated at a high temperature to improve the abrasion resistance inPatent document 1. Therefore, the technology disclosed in Patentdocument 1 by itself cannot achieve both abrasion resistance improvementand thermal deformation suppression at a high temperature.

Patent document 1 doesn't disclose any suggestion of suppressing thermaldeformation at a high temperature, as only disclosing running stabilityin page 20 describing the change of elongation ratio from 2%-relaxationrate to 10%-stretch rate about high-temperature heat treatment of liquidcrystal polyester fiber after solid-phase polymerization. It doesn'teven disclose any suggestion of advantage of a guide provided after theheat treatment with respect to the running stability for the heattreatment.

Page 2 of Patent document 2 discloses a technology in which liquidcrystal polyester fiber after solid-phase polymerization is subject to athermal stretch by 10% or more as a high-temperature heat treatment.However, Patent document 2 doesn't disclose any suggestion to suppress athermal deformation at a high temperature, as only disclosing thepurpose of the stretch, such as abrasion resistance improvement andthinning by stretching fiber.

Page 15 of Patent document 3 discloses a technology to thermally stretchthe liquid crystal polyester fiber before solid-phase polymerization byless than 1.005 ratio. With this technology, the liquid crystalpolyester fiber is stretched before the solid-phase polymerization at arelatively low temperature of the glass transition temperature+50° C. orless, while it discloses neither the improvement of abrasion resistanceby the heat treatment at a high temperature of the melting point+50° C.or more nor the suggestion about thermal deformation at the hightemperature. Although Patent document 3 discloses a dynamic viscoelasticmeasurement of tan δ to obtain Tg (glass transition temperature) of theresin, it doesn't disclose any relation between tan δ and thermaldeformation suppression at a high temperature.

Page 2 of Patent document 4 discloses a technology of solid-phasepolymerization (heat treatment) of liquid crystal polyester fiberperformed at a temperature of Tm−80° C. or less, and subsequently atanother temperature between Tm−60° C. and Tm+20° C. With thistechnology, the temperature for solid-phase polymerization is raisedstepwise to improve a vibration damping characteristics, while itdiscloses neither the improvement of abrasion resistance by the heattreatment at a high temperature of the melting point+50° C. or more northe suggestion about thermal deformation at the high temperature.Although Patent document 4 discloses tan δ measured as an index torepresent vibration damping characteristics of solid-phase polymerizedliquid crystal polyester fiber, it doesn't disclose any relation betweentan δ of liquid crystal polyester fiber prepared by a high-temperatureheat treatment at the melting point+50° C. or more and thermaldeformation suppression at a high temperature.

PRIOR ART DOCUMENTS Patent Documents

-   Patent document 1: JP2008-240230-A-   Patent document 2: JP2010-189819-A-   Patent document 3: JP2006-89903-A-   Patent document 4: JP-H4-289218-A

Non-Patent Documents

-   Non-patent document 1: “Reforming technology and the latest    applications of liquid crystal polymer”, edited by Technical    information institute, Co., Ltd, pp. 235-256 (2006)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As an object of our invention, it could be helpful to provide a liquidcrystal polyester fiber having high strength, high elastic modulus, highabrasion resistance, excellent processability and less heat deformationat a high temperature, and a manufacturing method thereof.

Means for Solving the Problems

The above-described object of our invention can be achieved by thefollowing means.

(1) A liquid crystal polyester fiber having: a peak half-value width of15° C. or more at an endothermic peak (Tm1) observed by a differentialcalorimetry under a temperature elevation condition of 20° C./min from50° C.; a weight-average molecular weight in terms of polystyrene of250,000 or more and 2,000,000 or less; a peak temperature of a losstangent (tan δ) of 100° C. or more and 200° C. or less; and a peak valueof the loss tangent (tan δ) of 0.060 or more and 0.090 or less.(2) A mesh fabric comprising the liquid crystal polyester fiber of (1).(3) A producing method of a melt-spun liquid crystal polyester fibercharacterized in that a liquid crystal polyester fiber made by a meltspinning is polymerized in a solid phase and then heated at atemperature of an endothermic peak (Tm1)+50° C. or more by a stretchrate of 0.1% or more and less than 3.0%, wherein the endothermic peak isobserved by a differential calorimetry under a temperature elevationcondition of 20° C./min from 50° C.

Effect According to the Invention

Our liquid crystal polyester fiber can be excellent in abrasionresistance and processability, so that the weaving performance inproducing a product such as mesh fabric is enhanced to reduce faults inthe product. Further, it has a small thermal deformation even at a hightemperature, so that a fabric product has only a small variation inperformance and dimension through the high-temperature treatment.Furthermore, the producing method of our invention can produce theliquid crystal polyester fiber efficiently.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, our liquid crystal polyester fiber will be explained indetails.

The liquid crystal polyester described in the specification means apolyester capable of forming an anisotropic melting phase (liquidcrystallinity) when molten. This characteristic can be recognized byobserving light transmitted through the sample under polarized radiationwhen a sample of liquid crystal polyester is placed on a hot stage andheated in nitrogen atmosphere, for example.

The liquid crystal polyester in the specification may be:

a) a polymer of an aromatic oxycarboxylic acid component;

b) a polymer of an aromatic dicarboxylic acid component, an aromaticdiol component and/or an aliphatic diol component; and

c) a copolymer of a) and b).

It is preferable that the liquid crystal polyester is a wholly aromaticpolyester prepared without the aliphatic diol component for achievinghigh strength, high elastic modulus and high heat resistance. Thearomatic oxycarboxylic acid component may be an aromatic oxycarboxylicacid such as hydroxy benzoic acid and hydroxy naphthoic acid, and may bealkyl, alkoxy or halogen substitution product of the aromaticoxycarboxylic acid. The aromatic dicarboxylic acid component may be anaromatic dicarboxylic acid such as terephthalic acid, isophthalic acid,diphenyl dicarboxylic acid, naphthalene dicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethane dicarboxylic acid and diphenylethanedicarboxylic acid, and may be alkyl, alkoxy or halogen substitutionproduct of the aromatic dicarboxylic acid. The aromatic diol componentmay be an aromatic diol component such as hydroquinone, resorcinol,dioxydiphenyl and naphthalene diol, and may be alkyl, alkoxy or halogensubstitution product of the aromatic diol. The aliphatic diol componentmay be an aliphatic diol such as ethylene glycol, propylene glycol,butane diol and neopentyl glycol.

It is preferable that the liquid crystal polyester is a copolymer ofp-hydroxy benzoic acid component, 4,4′-dihydroxy biphenyl component,hydroquinone component, terephthalic acid component and/or isophthalicacid component, a copolymer of p-hydroxy benzoic acid component and6-hydroxy 2-naphthoic acid component, a copolymer of p-hydroxy benzoicacid component, 6-hydroxy 2-naphthoic acid component, hydroquinonecomponent and terephthalic acid component or the like, for achievingexcellent spinnability, high strength, high elastic modulus, andabrasion resistance improved by high-temperature heat treatment aftersolid-phase polymerization.

It is preferable that the liquid crystal polyester comprises thefollowing structural units (I), (II), (III), (IV) and (V). Besides,“structural unit” means a unit capable of composing repeated structuresin a main chain of polymer in the specification.

This combination of structural units makes it possible for the molecularchain to have a proper crystallinity and a non-linearity, namely, amelting point capable of being melt spun. Therefore a good yarn-makingproperty can be exhibited at a spinning temperature set between themelting point and the thermal decomposition temperature of polymer, asproviding fiber uniform along the longitudinal direction, while thestrength and elastic modulus of fiber can be enhanced with appropriatecrystallinity.

Further, it is important to combine components of diol with a highlinearity and such a small bulk as structural units (II) and (III), sothat the molecular chain in the fiber can have an orderly structure withless disorder while the crystallinity does not increase excessively andthe interaction in a direction perpendicular to the fiber axis can bemaintained. In addition to obtaining high strength and elastic modulusas such, particularly excellent abrasion resistance can be achieved bycarrying out a heat treatment at a high temperature after solid-phasepolymerization.

It is preferable the structural unit (I) is contained by 40 to 85 mol %,more preferably 65 to 80 mol %, further preferably 68 to 75 mol %, intotal of structural units (I), (II) and (III). By setting the content insuch a range, the crystallinity can be controlled properly, highstrength and elastic modulus can be achieved while the melting point canbe controlled in a range suitable for performing a melt spinning.

It is preferable that the structural unit (II) is contained by 60 to 90mol %, more preferably 60 to 80 mol %, further preferably 65 to 75 mol %in total of structural units (II) and (III). By setting the content insuch a range, since the crystallinity does not increase excessively andthe interaction in a direction perpendicular to the fiber axis can bemaintained, the abrasion resistance can be improved by carrying out aheat treatment at a high temperature after solid-phase polymerization.

It is preferable that the structural unit (IV) is contained by 40 to 95mol %, more preferably 50 to 90 mol %, further preferably 60 to 85 mol %in total of structural units (IV) and (V). By setting the content insuch a range, the melting point of the polymer can be controlledproperly, a good spinnability can be exhibited at a spinning temperatureset between the melting point and the thermal decomposition temperatureof the polymer, so that fiber uniform along the longitudinal directionis prepared. Further, since the linearity of the molecular chain loosensappropriately, the abrasion resistance can be improved while theinteraction in a direction perpendicular to the fiber axis can beenhanced with a fluctuant fibril structure by carrying out a heattreatment at a high temperature after solid-phase polymerization.

Preferred ranges of the respective structural units of the liquidcrystal polyester are as follow. Desirable liquid crystal polyesterfiber can be obtained by controlling the composition in these ranges soas to satisfy the above-described condition.

Structural unit (I): 45-65 mol %Structural unit (II): 12-18 mol %Structural unit (III): 3-10 mol %Structural unit (IV): 5-20 mol %Structural unit (V): 2-15 mol %

In addition to the above-described structural units, it is possible tocopolymerize an aromatic dicarboxylic acid such as 3,3′-diphenyldicarboxylic acid and 2,2′-diphenyl dicarboxylic acid, an aliphaticdicarboxylic acid such as adipic acid, azelaic acid, sebacic acid anddodecanedionic acid, an alicyclic dicarboxylic acid such as hexahydroterephthalic acid (1,4-cyclohexane dicarboxylic acid), an aromatic diolsuch as chloro hydroquinone, 4,4′-dihydroxy phenylsulfone,4,4′-dihydroxy diphenylsulfide and 4,4′-dihydroxy benzophenone,p-aminophenol or the like, in the liquid crystal polyester by 5 mol % orless as far as advantages of our invention are achieved.

It is possible to add a polyester, a vinyl-based polymer such aspolyolefin and polystyrene, or another polymer such as polycarbonate,polyamide, polyimide, polyphenylene sulfide, polyphenylene oxide,polysulfone, aromatic polyketone, aliphatic polyketone, semi-aromaticpolyester amide, polyetheretherketone and fluororesin. It is preferableto add polyphenylene sulfide, polyetheretherketone, nylon 6, nylon 66,nylon 46, nylon 6T, nylon 9T, polyethylene terephthalate, polypropyleneterephthalate, polybutylene terephthalate, polyethylene naphthalate,polycyclohexane dimethanol terephthalate, polyester 99M or the like.From a viewpoint of good yarn-making property, it is preferable thatsuch a polymer has a melting point within a range of the melting pointof the liquid crystal polyester±30° C.

It is possible to add a small amount of an inorganic substance such asvarious metal oxides, kaoline and silica or an additive such ascolorant, delustering agent, flame retardant, anti-oxidant, ultravioletray absorbent, infrared ray absorbent, crystal nucleus agent,fluorescent whitening agent, end-group closing agent and compatibilizingagent as far as advantages of our invention are achieved.

The liquid crystal polyester fiber should have a weight averagemolecular weight (may be called merely “molecular weight”) of 250,000 to2,000,000 in terms of polystyrene. The high molecular weight of 250,000or more contributes to high strength, elastic modulus and elongation.Because the strength, elastic modulus and elongation are likely toincrease as the molecular weight becomes higher, it is preferable thatthe molecular weight is 300,000 or more, preferably 350,000 or more. Theupper limit of molecular weight may be around 2,000,000 and may besufficient at 1,000,000. The molecular weight is determined by themethod to be explained in the Example.

The liquid crystal polyester fiber should have 15° C. or higher of peakhalf-value width observed by differential calorimetry under temperatureelevation condition of 20° C./min from 50° C. Tm1 in this determinationmethod represents a melting point of fiber. The wider the area of thepeak shape is, or the greater the heat of melting (ΔHm1) is, the higherthe crystallinity is. Also the smaller the half-value width is, thehigher the completeness of crystal is. By melt-spinning and thenpolymerizing the liquid crystal polyester in a solid-phase, Tm1elevates, ΔHm1 increases and the half-value width decreases, and thecrystallinity and completeness of crystal increases, so that the fiberincreases in strength, elongation and elastic modulus as improving inheat resistance. On the other hand, the abrasion resistancedeteriorates, probably because a difference in structure between thecrystal part and the amorphous part becomes remarkable by increase ofthe completeness of crystal so that destruction occurs in the interfacetherebetween. Accordingly, while maintaining high Tm1 as well as highstrength, elastic modulus, elongation and heat resistance observed infiber which has been polymerized in a solid-phase, the crystallinity ofour fiber is decreased by increasing the peak half-value width above 15°C. observed in liquid crystal polyester fiber without solid-phasepolymerization, so that the abrasion resistance can be improved bydecreasing the difference in structure between the crystal/amorphousparts which becomes a trigger of the destruction as well as fluctuatingthe fibril structure to soften a whole fiber. It is preferable that thepeak half-value width at Tm1 is 20° C. or higher so that the greaterwidth makes the higher abrasion resistance. The upper limit of peakhalf-value width may industrially be around 80° C. and may be sufficientat 50° C.

Although only one endothermic peak is ordinarily observed in the liquidcrystal polyester fiber, there may be a case of observing two or moreendothermic peaks, when the fiber structure has been insufficientlysolid-phase polymerized. In such a case, the peak half-value width isdetermined as the sum of the half-value widths of respective peaks.

It is preferable that the melting point (Tm1) of fiber is 290° C. ormore, preferably 300° C. or more, and further preferably 310° C. ormore. Such a high melting point makes the heat resistance of fiberexcellent. To achieve such a high melting point of fiber, it is possiblethat a fiber is made from liquid crystal polyester having a high meltingpoint. It is preferable that a melt-spun fiber is polymerized in a solidphase so that the fiber has a high strength and elastic modulus as wellas excellent uniformity in a longitudinal direction. The upper limit ofmelting point may be around 400° C.

It is preferable that the heat of melting ΔHm1 is 6.0 J/g or less,although it varies depending upon the structural unit composition of theliquid crystal polyester. The ΔHm1 of 6.0 J/g or less can decrease thecrystallinity, fluctuates the fibril structure and softens the fiber asa whole, and decreases the difference in structure between thecrystal/amorphous parts which becomes a trigger of the destruction, sothat the abrasion resistance improves. It is preferable that the ΔHm1 is5.0 J/g or less so that the abrasion resistance improves. It ispreferable that the ΔHm1 is 0.2 J/g or more, for achieving high strengthand elastic modulus.

It is surprising that the ΔHm1 is 6.0 J/g or less in spite of highmolecular weight of 250,000 or more. The liquid crystal polyester havinga molecular weight of 250,000 or more is not fluidized with a remarkablyhigh viscosity and is difficult to be melt-spun even above the meltingpoint. A liquid crystal polyester fiber with such a high molecularweight can be obtained by melt spinning liquid crystal polyester havinga low molecular weight to be subject to solid-phase polymerization. Whenthe liquid crystal polyester fiber is subject to solid-phasepolymerization, the molecular weight increases, the strength,elongation, elastic modulus and heat resistance improve, and thecrystallinity also increases, so that the ΔHm1 increases. When thecrystallinity increases, the strength, elongation, elastic modulus andheat resistance further increase, although the difference in structurebetween the crystal part and the amorphous part becomes remarkable, theinterface therebetween is liable to be destroyed, and the abrasionresistance decreases. However in our invention, the high strength,elastic modulus and heat resistance can be maintained by having such ahigh molecular weight as characterized in a solid-phase polymerizedfiber while the abrasion resistance can be increased by having such alow crystallinity or such a low ΔHm1 as observed in liquid crystalpolyester without solid-phase polymerization. Our invention has achieveda technical advance improving the abrasion resistance by a structurechange such as decreased crystallinity.

It is preferable that the Tm2 of the fiber is 300° C. or more from aviewpoint of enhanced heat resistance. The upper limit of Tm2 may bearound 400° C.

It is preferable that the ΔHm2 is 5.0 J/g or less, preferably 2.0 J/g orless, because the excessive ΔHm2 might increase the crystallinity as apolymer itself and make it difficult to improve the abrasion resistance.Although only one endothermic peak is ordinarily observed in the liquidcrystal polyester fiber when it is heated again after a cooling processin the above-described measurement condition, there may be a case ofobserving two or more endothermic peaks. In such a case, the ΔHm2 isdetermined as the sum of ΔHm2 of respective peaks.

The fiber has a peak temperature of loss tangent (tan δ) of 100° C. to200° C. preferably 120° C. to 180° C. while it has a peak value of 0.060to 0.090. In the specification, the peak temperature of tan δ and peakvalue are determined by the method to be described in Examples.

The tan δ is a ratio of loss elastic modulus to storage elastic modulus.When the tan δ is high the ratio of heat scatter per energy applied ishigh. It is thought that a peak appears in temperature dependence of tanδ in a synthetic fiber, and the peak temperature has significance likethe glass transition temperature as a temperature at which kineticism ofamorphous part begins to increase while the peak value has significancelike the amount of the amorphous part itself.

The liquid crystal polyester fiber has a low crystallinity since it hasbeen heat-treated at a high temperature after solid-phasepolymerization, so that it consists primarily of the amorphous part andhas a clear peak in the tan δ. The peak value corresponds to the amountof amorphous part and therefore the one having a high peak value has agreat amount of amorphous part and tends to deform thermally. Namely, tosuppress the thermal deformation, it is preferable that the peaktemperature of tan δ is high and the peak value is low. On the otherhand, to achieve a high abrasion resistance characterizing the fiber ofour invention, it is preferable that the peak value is high so that thecrystallinity of polymer is low. To achieve such conflictingcharacteristics at the same time, it is necessary to set the tan δproperly.

The tan δ peak value of the fiber should be 0.090 or less. The peakvalue of 0.090 or less can suppress thermal deformation at a hightemperature. It is preferable that the peak value is 0.085 or less sothat the thermal deformation is suppressed more. To prevent the abrasionresistance from deteriorating by a high crystallinity derived from anexcessively low peak value, it is preferable that the peak value is0.060 or more, preferably 0.065 or more.

The peak temperature of tan δ is a temperature at which the kineticismof amorphous part suddenly increases. The temperature above the peaktemperature might cause a thermal deformation. Therefore, the peaktemperature is preferably higher. The peak temperature of the fibershould be 100° C. or more, preferably 130° C. or more. The upper limitof peak temperature may be around 200° C.

As described later, such desirable peak temperature and peak value oftan δ can effectively be achieved by properly setting a stretch rate ina heat treatment after solid-phase polymerization.

To enhance the strength of mesh fabric, it is preferable that the liquidcrystal polyester fiber has a strength of 12.0 cN/dtex or more,preferably 14.0 cN/dtex or more, further preferably 15.0 cN/dtex ormore. The upper limit of strength may be around 30.0 cN/dtex.

It is preferable that the fiber has a strength fluctuation rate of 10%or less, preferably 5% or less. The strength in the specification meansstrength at a cutting process in measuring a tensile strength describedin JIS L1013:2010. The strength fluctuation rate is measured by themethod to be described in Examples. The uniformity along a longitudinaldirection is enhanced and the fluctuation of fiber strength (product ofstrength and fineness) is decreased by the strength fluctuation rate of10% or less, so that defects of fiber product reduce and yarn breakagederived from a low strength portion in a higher processing can also besuppressed.

To enhance the elastic modulus of fabric, it is preferable that theelastic modulus of fiber is 500 cN/dtex or more, preferably 600 cN/dtexor more, further preferably 700 cN/dtex or more. The upper limit ofelastic modulus may be around 1200 cN/dtex.

It is preferable that the fiber has an elongation of 1.0% or more,preferably 2.0% or more. The elongation of 1.0% or more can enhance theimpact absorbency of fiber to improve the abrasion resistance, and canmake the processability in a higher processing and handling abilityexcellent. The upper limit of elongation may be around 10.0%. The fiberhaving a molecular weight of 250,000 or more can have a high elongation.

In the specification, strength, elongation and elastic modulus aredetermined by the method to be described in Examples.

Because of its high strength and elastic modulus, the fiber can besuitably used in applications, such as printing screen gauzes and meshesfor filter. Also, because a high strength can be exhibited even withthin fiber fineness, it can be achieved to make a fibrous materialsmaller in weight and thickness, and a yarn breakage in a higherprocessing such as weaving process can also be suppressed. The fiberhaving a molecular weight of 250,000 or more can have a high strengthand elastic modulus.

It is preferable that the fiber has a single fiber fineness of 18.0 dtexor less. Such a thin single fiber fineness of 18.0 dtex or less, canmake the molecular weight easily increase to improve in strength,elongation and elastic modulus when polymerized in a solid phase atfibrous state. Further, it makes possible that the flexibility and theworkability of fiber are improved, that the surface area increases toenhance the adhesion property with chemical agents such as an adhesive.Furthermore, it makes possible that the thickness becomes thinner, thatthe weave density is increased, and that the opening (area of openingpart) can be widened in case of being formed as a gauze comprisingmonofilaments. The single-fiber fineness is more preferably 15.0 dtex orless, and further preferably 10.0 dtex or less. The lower limit ofsingle fiber fineness may be around 1.0 dtex.

It is preferable that the fiber has a birefringent rate (Δn) of 0.250 ormore and 0.450 or less. Such a range of the Δn can make the fiber axialmolecular orientation sufficiently high to achieve high strength andelastic modulus.

It is preferable that the fiber has an abrasion resistance C of 60 secor more, preferably 90 sec or more, further preferably 180 sec or more.The abrasion resistance C is determined by the method to be described inExamples. The abrasion resistance C of 60 sec or more can make itpossible that fibrillation of liquid crystal polyester fiber at a higherprocessing is suppressed, that deterioration of the processability andweaving performance causes by fibril accumulation is suppressed, thatthe clogging of opening due to accumulated fibrils being woven thereinis suppressed, and that less deposition of fibrils onto guides extendsthe cycle for cleaning or exchange.

It is preferable that the fiber has a thermal deformation rate at a hightemperature of 1.0% or less. The thermal deformation rate of 1.0% orless can maintain a product performance even after a high-temperatureheat treatment. It is preferable that the thermal deformation rate is0.7% or less. The lower limit of thermal deformation rate may be around0.2%.

To make fiber products thinner and lighter, it is preferable that thefiber has the number of filaments of 50 or less, preferably 20 or less.In particular, such a fiber can be suitably used in the technical fieldof monofilament having the number of filaments of 1 requiring high fiberfineness, high strength, high elastic modulus and high uniformity ofsingle fiber fineness.

It is preferable that the fiber has a yarn length of 40,000 m or more.The length of 40,000 m can minimize faults caused by connecting yarns inproduct-making process such as weaving process. The upper limit of yarnlength may be around 10,000,000 m although the longer is the morepreferable. Such a long yarn length of fiber can effectively be preparedunder conditions of a proper stretch rate and a good running stabilityachieved by regulating a yarn route with a guide after heat treatment.

A mesh fabric can be made from the liquid crystal polyester fiber. Sincethe liquid crystal polyester fiber is excellent in abrasion resistanceand processability, the weaving performance in making a product such asa mesh fabric is enhanced to make the product with less faults. Further,the thermal deformation is small even at a high temperature, so that theproduct doesn't change greatly in dimension and performance even in ahigh-temperature processing.

The liquid crystal polyester fiber has a high strength, high elasticmodulus and high abrasion resistance and a small thermal deformation,and is excellent in processability, so that it can be used in variousfields such as general industrial material, civil engineering andconstruction material, sport material, protective clothing material,rubber-reinforcing material, electric material (tension members inparticular), acoustic material and general clothing material. It cansuitably be used for screen gauzes, filters, ropes, nets, fishing nets,computer ribbons, base fabrics for printed boards, canvases for papermachines, air bags, air ships, base fabrics for domes or the like, ridersuits, fishlines, various lines (lines for yachts, paragliders,balloons, kite yarns or the like), blind cords, support cords for wirescreens, various cords in automobiles or air planes, power transmissioncords for electric equipment or robots or the like. It can beparticularly suitable as woven fabrics for industrial materialscomprising monofilaments such as preferably used for printing screengauzes and filters, for such monofilaments which strongly require highstrength, high elastic modulus and thin fineness as well as goodabrasion resistance for improving weaving performance and fabricquality.

Hereinafter a method for producing the liquid crystal polyester fiberwill be explained.

The composition and desirable composition ratio of the liquid crystalpolyester have been described in the part explaining fibers.

To make a wider temperature range capable of melt spinning, it ispreferable that a melting point of the liquid crystal polyester is 200to 380° C., and is preferably 250 to 360° C. for enhancing spinnability.The melting point of the liquid crystal polyester polymer means a value(Tm2) measured by the method to be described in Examples.

It is preferable that the liquid crystal has a weight average molecularweight (may be called “molecular weight”) of 30,000 or more in terms ofpolystyrene. The molecular weight of 30,000 or more can enhance theyarn-making property with an adequate viscosity at a spinningtemperature. When the molecular weight is too high, the viscositybecomes high and the flowability deteriorates although the strength,elongation and elastic modulus of the fiber are enhanced, and ultimatelyit becomes impossible to flow. Therefore it is preferable that themolecular weight is 250,000 or less, preferably less than 200,000 orless. The weight average molecular weight in terms of polystyrene isdetermined by the method to be described in Examples.

It is preferable that the liquid crystal polyester is dried before beingmelt spun, from a viewpoint of suppressing bubbling caused by watermixture and of enhancing yarn-making property. It is more preferablethat vacuum drying is performed, because the monomer which remains inthe liquid crystal polyester can be removed, so that yarn-makingproperty is further enhanced. The vacuum drying is usually performed at100-200° C. for 8-24 hours.

To prevent a systematic structure from being produced at the time ofpolymerization in the melt spinning, it is preferable to use anextruder-type extruding machine although any known method can beemployed for melt extrusion of liquid crystal polyester. The extrudedpolymer is metered by a known metering device, such as a gear pumpthrough a pipe, and is introduced into a spinneret after passing througha filter for removing foreign materials. It is preferable that thetemperature (spinning temperature) from the polymer pipe to thespinneret is controlled above the melting point of the liquid crystalpolyester, preferably controlled to a temperature of the melting pointof the liquid crystal polyester+10° C. or more. It is preferable thatthe spinning temperature is 500° C. or less, preferably 400° C. or less,in case that the spinning temperature is so high that the viscosity ofthe liquid crystal polyester increases to deteriorate fluidity andyarn-making property. It is possible to individually adjust thetemperature at each portion from the polymer pipe to the spinneret. Inthis case, the discharge can be stabilized by controlling thetemperature of a portion near the spinneret as higher than thetemperature of an upstream portion thereof.

To enhance the yarn-making property and uniformity of fineness with thedischarge, it is preferable that the spinneret has a hole of smalldiameter and a long land length (length of a straight pipe part havingthe same inner diameter as the hole of the spinneret). It is preferablethat the hole diameter is 0.05 mm or more and 0.50 mm or less,preferably 0.10 mm or more and 0.30 mm or less, in case that anexcessively small hole diameter might cause a clogging of holes. It ispreferable that an L/D defined as a quotient calculated by dividing landlength L with hole diameter D is 1.0 or more and 3.0 or less, preferably2.0 or more and 2.5 or less, in case that an excessively long landlength might increase a pressure loss.

To maintain the uniformity, it is preferable that the spinneret hasholes of 50 or less, preferably 20 or less. It is preferable that anintroduction hole positioned right above the hole of the spinneret isstraight shaped hole, from a viewpoint of preventing the increasedpressure loss. It is preferable that the introduction hole and thespinneret hole are connected with a tapered portion to suppress abnormalretention.

The polymer discharged from the spinneret holes passes through heatretention region and cooling region and is solidified and then is drawnup by a roller (godet roller) rotating at a constant speed. It ispreferable that the heat retention region extends by a length of 200 mmor less from the spinneret surface, preferably 100 mm or less, becausethe yarn-making property deteriorates by an excessively long heatretention region. When the atmosphere temperature in the heat retentionregion is raised with a heating means, it is preferable that theatmosphere temperature is 100° C. or more and 500° C. or less,preferably 200° C. or more and 400° C. or less. The polymer can becooled with inert gas, air, steam or the like. To reduce theenvironmental load and energy, it is preferable that it is cooled withair flow at room temperature (20-30° C.) blown in parallel or annularly.

From viewpoints of improved productivity and thinner single-yarnfineness, it is preferable that the draw velocity (spinning velocity) is50 m/min or more, preferably 500 m/min or more. Since the desirableliquid crystal polyester has a good spinnability at a spinningtemperature, the upper limit of draw velocity may be around 2,000 m/min.

It is preferable that a spinning draft defined as a quotient calculatedby dividing a draw velocity with a discharge linear velocity is 1 ormore and 500 or less, and is more preferably 10 or more and 100 or lessto enhance a yarn-making property and uniformity of fineness.

In a melt spinning process, it is preferable that oil solution isapplied between a cooling-solidification step of polymer and a take-upstep so that the handling property of fiber is improved. The oilsolution may be a known oil solution and is preferably a generalspinning oil solution or a mixed oil solution of inorganic particle (A)and phosphate compound (B) to be described later, in order to improve anunraveling-property to unravel a fiber (hereinafter called raw yarn ofspinning) prepared by melt-spinning at a roll-back step beforesolid-phase polymerization.

The take-up may be carried out by using a known winder to form a packagesuch as pirn, cheese and cone. To prevent a fiber from fibrillating withfriction, it is preferable to employ a pirn winding in which a rollerdoesn't contact a package surface when the fiber is taken up.

It is preferable that the melt-spun fiber has a single fiber fineness of18.0 dtex or less. The single fiber fineness is determined by the methodto be described in Examples. The single fiber fineness of 18.0 dtex orless can increase the molecular weight of polymer constituting the fiberat the time of solid-phase polymerization in a fiber state, so thatstrength, elongation and elastic modulus are improved. Further, thesurface area can be wider to increase the adhesion amount of fusioninhibitor of inorganic particle (A) and phosphate compound (B). It ispreferable that the single fiber fineness is 10.0 dtex or less,preferably 7.0 dtex or less. The lower limit of single fiber finenessmay be around 1.0 dtex.

It is preferable that the melt-spun fiber has a strength of 3.0 cN/dtexor more, preferably 5.0 cN/dtex or more so that the processability isenhanced by preventing yarn breakage in a roll-back process before thesolid-phase polymerization. The upper limit of strength may be around 10cN/dtex.

It is preferable that the melt-spun fiber has an elongation of 0.5% ormore, preferably 1.0% or more so that the processability is enhanced bypreventing yarn breakage in a roll-back process before the solid-phasepolymerization. The upper limit of elongation may be around 5.0%.

It is preferable that the melt-spun fiber has an elastic modulus of 300cN/dtex or more, preferably 500 cN/dtex or more so that theprocessability is enhanced by preventing yarn breakage in a roll-backprocess before the solid-phase polymerization. The upper limit ofelastic modulus may be around 800 cN/dtex.

The strength, elongation and elastic modulus are determined by themethod to be described in Examples.

It is preferable that the melt-spun fiber has a molecular weight of30,000 or more. The molecular weight of 30,000 or more can achieve ahigh strength, elongation and elastic modulus with excellentprocessability. It is preferable that the molecular weight is 250,000 orless, preferably 200,000 or less, because excessively high molecularweight might slow the solid-phase polymerization to fail to have a highmolecular weight achieved. The weight average molecular weight in termsof polystyrene is determined by the method to be described in Examples.Besides, the molecular weight doesn't tend to fluctuate greatly in amelt spinning process.

Then the melt spun fiber is subject to solid-phase polymerization afterfusion inhibitor oil solution is applied to the fiber. To enhance theadhesion efficiency, it is preferable that the fusion inhibitor isapplied to the fiber yarn while a melt spun fiber yarn taken up isrolled back, or that the fusion inhibitor is applied in a small amountto the melt spun fiber yarn and then is applied additionally to thefiber while the taken-up fiber yarn is rolled back, although the fusioninhibitor may be applied to the fiber between the melt spinning andtake-up processes.

To make the fusion inhibitor uniformly adhere to a fiber such asmonofilament having a thin total fineness, it is preferable that thefusion inhibitor is applied with a kiss roll (oiling roll) made of metalor ceramic, although a guide-feed method may be employed for theadhesion. A hank or a tow of fiber can be applied by immersing it in amixed oil solution.

It is preferable that the fusion inhibitor is a mixture of inorganicparticle (A) and phosphate compound (B). The mixture of inorganicparticle (A) and phosphate compound (B) applied can suppress the fusionbetween fibers in solid-phase polymerization and thermally denature thecomponents in the solid-phase polymerization process, to achieveexcellent processability in the following process and excellentpost-workability to make a product. In the specification, the fusioninhibitor made of inorganic particle (A) and phosphate compound (B) iscalled “oil solution for solid-phase polymerization”, “mixed oilsolution” or “oil solution” for convenience although such an oilsolution doesn't contain any oil component.

The inorganic particle (A) in the specification is a known inorganicparticle and may be mineral, metal hydroxide such as magnesiumhydroxide, metal oxide such as silica and alumina, carbonate compoundsuch as calcium carbonate and barium carbonate, sulfate compound such ascalcium sulfate or barium sulfate, carbon black, or the like. Such aheat-resistant inorganic particle is applied onto the fiber to reducecontact areas between single fibers in solid-phase polymerization, sothat fusion is prevented in the solid-phase polymerization process.

It is preferable that the inorganic particle (A) is easily handled toperform the application process while it is easily dispersed in water toreduce environmental load and is inert under a solid-phasepolymerization condition. From these viewpoints, it is preferable toemploy silica or mineral of silicate. It is preferable that the mineralof silicate is a phyllo-silicate having a layer structure. Thephyllo-silicate may be kaolinite, halloysite, serpentine, garnierile,smectites, pyrophyllite, talc, mica or the like. From a viewpoint ofavailability, it is most preferable to employ talc or mica.

The phosphate compound (B) may be a compound identified by any one offollowing chemical formulae (1)-(3).

Here, R1 and R2 indicate hydrocarbon, M1 indicates alkali metal, M2indicates any one of alkali metal, hydrogen, hydrocarbon andoxygen-containing hydrocarbon. Besides n indicates an integer of 1 ormore. From a viewpoint of suppressing thermolysis, it is preferable thatthe upper limit of n is 100 or less, preferably 10 or less.

From a viewpoint of reducing the environmental load of gas generatedwith thermolysis in solid-phase polymerization, it is preferable thatthe R1 has no phenyl group in the structure and preferably consists ofalkyl group. From a viewpoint of affinity to the fiber surface, it ispreferable that the R1 has a carbon number of 2 or more. From aviewpoint of suppressing the weight reduction rate caused bydecomposition of organic components accompanied with solid-phasepolymerization to prevent carbide generated by the decomposition in thesolid-phase polymerization process from remaining on the fiber surface,it is preferable that the carbon number is 20 or less.

From a viewpoint of water solubility, it is preferable that the R2 is ahydrocarbon having a carbon number of 5 or less, preferably 2 or 3.

From a viewpoint of production cost, it is preferable that the M1 issodium or potassium.

Using both inorganic particle (A) and phosphate compound (B) can enhancethe dispersibility of inorganic particle (A) and enable uniformapplication to fiber to exhibit excellent suppression of fusion andadhesion of inorganic particle (B) onto the fiber surface, so thatdecreased amount of inorganic particle (A) remains on the fiber after awashing process and then fouling is suppressed in the followingprocessing.

Further, phosphate compound (B) can easily be removed with water fromfiber in the washing process after solid-phase polymerization, throughgenerating condensed phosphate salt with dehydration and decompositionof organic components contained in phosphate compound (B) under asolid-phase polymerization condition. When phosphate compound (B) issolely applied to fiber, the deliquescence of the condensed salt mightmake the phosphate salt absorb moisture to deliquesce on the fibersurface even under an ordinary fiber storage condition, so thatwashability deteriorates because of increased viscosity. Namely, theexcellent washability is exhibited by using both inorganic particle (A)and phosphate compound (B). We presume such an excellent washability isexhibited by a mechanism in which inorganic particle (A) having a goodabsorbency prevents the condensed salt of phosphate compound (B) fromnaturally absorbing moisture to deliquesce and the condensed salt ofphosphate compound (B) absorbs water to expand as running in water, soas to fall off the fiber surface by layer fractions.

To uniformly apply inorganic particle (A) and phosphate compound (B) tofiber by an adequate adhesion amount, it is preferable to employ a mixedoil solution made by adding inorganic particle (A) to diluted solutionof phosphate compound (B) which is preferably diluted with water forsafety. From a viewpoint of suppressing fusion, it is preferable thatthe concentration of inorganic particle (A) is as high as 0.01 wt % ormore, preferably 0.1 wt % or more and that the upper limit is 10 wt % orless, preferably 5 wt % or less for uniform dispersion. From a viewpointof uniform dispersion, it is preferable that the concentration ofphosphate compound (B) is as high as 0.1 wt % or more, preferably 1.0 wt% or more. To prevent the mixed oil solution from excessive adhesioncaused by increased viscosity and adhesive spotting caused bytemperature dependency of viscosity, it is preferable that theconcentration of phosphate compound (B) is 50 wt % or less, preferably30 wt % or less.

It is preferable that “a” defined as adhesion rate of inorganic particle(A) and “b” defined as adhesion rate of phosphate compound (B) satisfythe following conditions.

Condition 1: 30≥a+b≥2.0Condition 2: a≥0.05Condition 3: b/a≥1

In Condition 1, it is preferable that the oil adhesion rate (a+b) of oilsolution for solid-phase polymerization is 2.0 wt % or more forsuppressing fusion, and is 30 wt % or lower in case that excessiveadhesion rate might make fiber sticky to deteriorate the handlingability. It is more preferably 4.0 wt % or more and 20 wt % or less.Here, the oil adhesion rate (a+b) of oil solution for solid-phasepolymerization is determined by the method to be described in Examplesfor fiber after applying the oil solution for solid-phasepolymerization.

In Condition 2, the adhesion rate (a) of inorganic particle of 0.05 wt %or more can suppress fusion by inorganic particles remarkably. The upperlimit of adhesion rate (a) may be around 5 wt % or less, from aviewpoint of uniform adhesion.

In Condition 3, it is preferable that adhesion rate (b) of phosphatecompound (B) is equal to or more than adhesion rate (a) of inorganicparticle (A), so that the adhesion between inorganic particle (A) andfiber is suppressed while excellent washability is exhibited remarkablyas derived from generating condensed salt in solid-phase polymerizationof phosphate compound (B).

Here, adhesion rate (a) of inorganic particle (A) and adhesion rate (b)of phosphate compound (B) are calculated by the following formula.

(Adhesion rate (a) of inorganic particle (A))=(a+b)×Ca/(Ca+Cb)

(Adhesion rate (b) of phosphate compound (B))=(a+b)×Cb/(Ca+Cb)

Here, Ca indicates a concentration of inorganic particle (A) in oilsolution for solid-phase polymerization, Cb indicates a concentration ofphosphate compound (B) in oil solution for solid-phase polymerization.

Next, the melt spun liquid crystal polyester fiber is subject tosolid-phase polymerization. The solid-phase polymerization can increasethe molecular weight to increase strength, elastic modulus andelongation. The solid-phase polymerization may be performed to a hank ortow of fiber (placed on a metal net or the like) or a continuous yarnbetween rollers. To simplify the apparatus and improve the productivity,it is preferable to be performed to a package made by taking up thefiber on a core.

When the solid-phase polymerization is performed to the package, thewinding density of fiber package in solid-phase polymerization should beimportant to prevent the fusion prevention. To prevent a windingcollapse, it is preferable that the winding density is 0.01 g/cc ormore. It is preferable that the winding density is 1.0 g/cc or less,preferably 0.8 g/cc or less to prevent the fusion-bonding. Here, thewinding density is calculated from fiber weight Wf [g] and occupiedvolume Vf [cc] of package obtained from outer size of package and corebobbin size. In case of package collapse by excessively small windingdensity, it is preferable that the winding density is 0.1 g/cc or more.The occupied volume Vf is determined by actually measuring the outersize of package or by calculating from the outer size measured onpicture as assuming that the package is rotationally symmetric. The Wfis determined by actually measuring the weight difference before andafter winding or by calculating from fineness and winding length.

It is preferable to form such a package having a small winding densitywhen the package has been taken up in melt spinning because theproductivity for apparatus and the efficiency of production can beimproved. On the other hand, it is preferable to make the windingdensity small when the package has been taken up in melt spinning andthen rolled back because the winding tension can be small for thesmaller winding density. Because the winding density can be smaller bythe smaller winding tension in the roll-back, it is preferable that thewinding tension is 0.50 cN/dtex or less, preferably 0.30 cN/dtex orless. The lower limit of winding density may be around 0.01 cN/dtex.

To decrease the winding density, it is preferable that the roll-backvelocity is 500 m/m or less, preferably 400 m/m or less. On the otherhand, a higher roll-back velocity is advantageous for productivity andit is preferable that the roll-back velocity is 50 m/m or more,preferably 100 m/m or more.

In order to form a stable package even with a low tension, it ispreferable that the winding formation is a taper-end winding providedwith tapered both ends. It is preferable that the taper angle is 70° orless, preferably 60° or less. When long fiber is required and the taperangle is too small to make a large fiber package, it is preferable thatthe taper angle is 1° or more, preferably 5° or more. In thespecification, the taper angle is defined by the following formula.

$\begin{matrix}{\theta = {\tan^{- 1}\left( \frac{2d}{l_{i} - l_{o}} \right)}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

θ: taper angle [°], d: winding thickness [mm], innermost stroke [mm],lo: outermost stroke [mm]

The winding number is also important for forming a package. The windingnumber means the number of times of rotation of a spindle during halfreciprocation of a traverse. It is defined as a product of a time forthe half reciprocation of a traverse [min] and the rotational speed of aspindle [rpm]. The greater winding number indicates the smaller traverseangle. A smaller winding number is advantageous for avoidingfusion-bonding because the contact area between fibers becomes smallerwhile a greater winding number makes a good shape of package by reducingthe package expansion and traverse failures at end faces. From theseviewpoints, it is preferable that the winding number is 2 or more and 20or less, preferably 5 or more and 15 or less.

The bobbin used for forming the fiber package may be any type bobbin aslong as it has a cylindrical shape, and it is attached to a winder whentaken up, and fiber is taken up to form a package by rotating it. Insolid-phase polymerization, although the fiber package may be treatedintegrally with the bobbin, the treatment may be carried out in acondition where only the bobbin is taken out from the fiber package.When the treatment is carried out in a condition where fiber is wound onthe bobbin, the bobbin should resist the temperature of solid-phasepolymerization and is preferably made of metal such as aluminum, brass,iron and stainless steel. It is preferable that many holes are opened onthe bobbin so that by-product of polymerization is removed quickly toperform solid-phase polymerization efficiently. When the treatment iscarried out in a condition where the bobbin is taken out from the fiberpackage, it is preferable that an outer skin is attached onto the outerlayer of bobbin. To prevent fusion between fiber in the innermost layerof package and bobbin outer layer in both cases, it is preferable thatcushion material is wound around the outer layer of bobbin onto whichliquid crystal polyester melt-spun fiber is taken up. It is preferablethat the cushion material is made of felt comprising organic fiber ormetal fiber, and has a thickness of 0.1 mm or more and 20 mm or less.The above-described outer skin may be replaced by the cushion material.

It is preferable that the fiber package has a yarn length (windingamount) of 10,000 m or more and 10,000,000 m or less.

The solid-phase polymerization may be performed under atmosphere ofinert gas such as nitrogen or atmosphere of active gas, such as air,containing oxygen, or under reduced pressure condition. To simplify theapparatus and prevent fiber or core material from oxidizing, it ispreferable that it is performed under nitrogen atmosphere. It ispreferable that the solid-phase polymerization is performed underatmosphere of low-humidity gas having a dew point of −40° C. or lower.

It is preferable that the maximum temperature of solid-phasepolymerization is Tm1−60° C., where Tm1 [° C.] is defined as anendothermic peak temperature of the liquid crystal polyester fiber to besubject to solid-phase polymerization. Such a high temperature aroundthe melting point makes it possible for the solid-phase polymerizationto progress immediately, so as to improve the fiber strength. The Tm1means a melting point of liquid crystal polyester fiber and isdetermined by the measurement method to be described in Examples. Toprevent fusion-bonding, it is preferable that the maximum temperature isless than Tm1 [° C.]. It is preferable that the solid-phasepolymerization temperature is increased stepwise or continuously totime, to prevent fusion-bonding and improve time efficiency ofsolid-phase polymerization. In this case, because the melting point ofthe liquid crystal polyester fiber increases together with progress ofsolid-phase polymerization, the solid-phase polymerization temperaturecan be raised up to Tm1+100° C. of the liquid crystal polyester fiberbefore solid-phase polymerization process. In this case, it ispreferable that the maximum temperature during solid-phasepolymerization is Tm1−60 [° C.] or more and less than Tm1 [° C.] of thefiber after solid-phase polymerization, so that the solid-phasepolymerization speed is increased and fusion-bonding is prevented.

To sufficiently enhance the molecular weight or strength, elasticmodulus and elongation of fiber, it is preferable that the solid-phasepolymerization time is 5 hours or more, preferably 10 hours or more. Onthe other hand, it is preferable that the time is 100 hours or less,preferably 50 hours or less to improve productivity because effects ofenhanced strength, elastic modulus and elongation are saturated overtime.

From viewpoints of processability in the higher processing andsuppressed faults in appearance of product, it is preferable thatsolid-phase polymerized fiber is washed. The fiber is washed to removeoil solution for solid-phase polymerization to prevent fusion-bonding,so that processability deterioration, which might be caused bydepositing the oil solution for solid-phase polymerization on guides ina post process such as weaving process, and fault generation, whichmight be caused by contaminating depositions in products, aresuppressed.

The washing method may be a method of wiping the fiber surface withcloth or paper. In case that the solid-phase polymerized yarn mightfibrillate with kinetic load, it is preferable to immerse the fiber in aliquid to which the oil solution for solid-phase polymerization issoluble or dispersible. It is more preferable that the washing isperformed by blowing off with fluid in addition to the immersing inliquid, so that the oil solution for solid-phase polymerization expandedwith liquid is removed efficiently.

It is preferable that the washing liquid is water for reducingenvironmental load. The liquid temperature should be higher forenhancing removal efficiency and is preferably 30° C. or more,preferably 40° C. or more. Because the liquid might evaporate remarkablywhen the liquid temperature is too high, it is preferable that theliquid temperature is the liquid boiling point−20° C. or less,preferably the liquid boiling point−30° C. or less.

From a viewpoint of washing efficiency improvement, it is preferablethat a surfactant is added to the washing liquid. To increase theremoval rate and decrease the environmental load, it is preferable thata surfactant is added by 0.01-1 wt %, preferably 0.1-0.5 wt %.

It is preferable that vibration or liquid flow is applied to a liquidfor washing to enhance washing efficiency. From viewpoints ofsimplifying the apparatus and saving energy, it is preferable that theliquid flow is applied to the liquid, although ultrasonic vibration maybe applied to the liquid. The liquid flow may be applied with a nozzleor by stirring in a liquid bath. It is preferable that it is appliedwith a nozzle so that the liquid is easily circulated with the nozzlethrough the liquid bath.

To increase the washing load per hour, it is possible that a hank, towor package of fiber is immersed in the liquid. It is preferable that thefiber running continuously is immersed in the liquid. The method toimmerse the fiber continuously may be performed by leading the fiberwith a guide or the like into the liquid bath. To suppress fibrillationof solid-phase polymerization caused by contact resistance to the guide,it is preferable that both ends are provided with a slit through whichfiber flows in the bath without yarn route guide.

Fiber is unraveled from a package of solid-phase polymerized yarncontinuously fed. To suppress fibrillation in delamination of slightfusion-bonding caused by solid-phase polymerization, it is preferablethat the yarn is unraveled in a direction (fiber-rounding direction)perpendicular to rotation axis by lateral-unraveling while thesolid-phase polymerized package is rotated.

Such an unraveling may be performed by a method such as forcing the yarnto be driven at a constant rotation speed by a motor or the like,controlling the rotation speed with a dancer roller to regulate theunraveling speed, and drawing the yarn from the solid-phase polymerizedpackage placed on a free roll with a speed-regulating roller to performthe unraveling. To remove oil efficiently, it is preferable that apackage of liquid crystal polyester fiber is immersed in the liquid andthen is unraveled as is.

It is preferable that the fluid used to blow off is air or water. It isparticularly preferable that the fluid is air to dry the surface ofliquid polyester fiber to improve yield by preventing contaminantdeposition in a post-processing.

Next, the solid-phase polymerized fiber is heat-treated at a temperatureof the melting point+50° C. or more. The melting point is Tm1 determinedby the method to be described in Examples. Hereinafter, the meltingpoint of fiber may be called Tm1. The abrasion resistance greatlyimproves when liquid crystal polyester fiber is heat treated at atemperature as high as Tm1+50° C. or more. The effect will becomeremarkable when the single fiber fineness is small.

A rigid molecular chain like liquid crystal polyester has a longrelaxation time and inner layer also relaxes within the relaxation timefor surface layer as melting the fiber. By studying technologiessuitable for liquid crystal polyester fiber to improve abrasionresistance, it was found that abrasion resistance of liquid crystalpolyester fiber can be improved by heating to reduce crystallinity andcrystal completeness as a whole fiber instead of relaxation of molecularchain.

To reduce crystallinity, fiber has to be heated above the melting point.However a thermoplastic synthetic fiber might reduce strength andelastic modulus and cause thermal deformation and fusion (meltdown) atsuch a high temperature particularly in case of small single-fiberfineness. Such a behavior was seen with liquid crystal polyester,however, we focused on the melting point of liquid crystal polyester asa temperature transiting from crystal to liquid crystal and found outthat increase of molecular weight of solid-phase polymerized liquidcrystal polyester has made relaxation time very long so that themolecular mobility of liquid crystal is low. Therefore even with ashort-time heat treatment at a high temperature above the melting point,the crystallinity can be reduced as keeping the orientation of molecularchains at a high level while the strength and the elastic modulus arenot greatly deteriorated. From these facts, it was found that liquidcrystal polyester fiber having a small single-yarn fineness can beimproved in abrasion resistance by a short-time heat treatment at a hightemperature above Tm1+50° C. without great loss of strength, elasticmodulus and heat resistance of liquid crystal polyester fiber.

To lower the crystal completeness for the solid-phase polymerized fiber,it is preferable that the heat treatment is performed at a temperatureof Tm1+60° C. or more, preferably Tm1+80° C. or more, most preferablyTm1+130° C. or more. In case that excessively high treatment temperaturemight increase the heat deformation of processed fiber at a hightemperature, it is preferable that the heat treatment is performed at atemperature of Tm1+200° C. or less, preferably Tm1+180° C. or less.

Although there is a case for carrying out a heat treatment for liquidcrystal polyester fiber even in a conventional technology, it isgenerally carried out at a temperature of the melting point or lessbecause the liquid crystal polyester is thermally deformed (fluidized)by stress even at a temperature of the melting point or less. Even whenthe solid-phase polymerization of liquid crystal polyester fiber isperformed as a heat treatment, the treatment temperature should be setbelow the melting point of fiber or the fiber might be fused and meltdown. In case of solid-phase polymerization, the final temperature ofsolid-phase polymerization may increase to a temperature higher than themelting point of fiber to be treated because the melting point of fibermay increase through the treatment. Even in this case, the treatmenttemperature is lower than the melting point of fiber being treated, thatis, the melting point of fiber after the heat treatment.

Such a high-temperature heat treatment, which doesn't mean thesolid-phase polymerization, increases abrasion resistance by decreasinga structural difference between a dense crystal portion formed bysolid-phase polymerization and an amorphous portion, namely bydecreasing the crystallinity and crystal completeness. Therefore even ifTm1 is varied by heat treatment, it is preferable that the heattreatment is performed at a temperature of Tm1, which is varied afterthe treatment, +50° C. or more, preferably the Tm1+60° C. or more,further preferably the Tm1+80° C. or more, most preferably the Tm1+130°C. or more.

Although heat stretching of liquid crystal polyester fiber may beincluded in the heat treatment, the heat stretching is a process tensingthe fiber at a high temperature, the orientation of molecular chain inthe fiber structure becomes high, the strength and the elastic modulusincrease, and the crystallinity and crystal completion are maintained asthey are, namely, high ΔHm1 is maintained and the small peak half-valuewidth of the melting point is maintained. Therefore it becomes a fiberstructure being inferior in abrasion resistance and such a heatstretching should be different from our heat treatment that aims toimprove the abrasion resistance by decreasing the crystallinity(decreasing ΔHm1) and decreasing the crystal completion (increasing thepeak half-value width). In our high-temperature heat treatment, thecrystallinity decreases so that strength and elastic modulus do notincrease.

It is preferable that the high-temperature heat treatment is performedas running fiber continuously, because the fusion-bonding between fiberscan be prevented and enhance the uniformity of the treatment. To preventfibrils from generating as achieving uniform treatment, it is preferablethat a non-contact heat treatment is performed. The heat treatment maybe performed by heating the atmosphere or a radiation heating with alaser or an infrared ray or the like. It is preferable that it isperformed with a slit heater having a block or a plate heater so thatboth advantages of atmosphere heating and radiation heating enhance thestability for the treatment.

The high-temperature heat treatment should be performed at a stretchrate of 0.1% or more and less than 3.0%. In the specification, thestretch rate is defined by the following formula with yarn velocity (V0)before heat treatment and yarn velocity (V1) after heat treatment. Theyarn velocities before and after heat treatment have the same meaning asthe surface velocities of roller regulating the yarn velocity before andafter heat treatment.

(Stretch rate [%])=(V1−V0)×100/V0

The stretching and relaxing in a high-temperature heat treatment havebeen described in prior art documents although that only meant a highstretch could make fiber thinner in addition to improvement of runningstability or abrasion resistance. However, it was found that stretchingin a heat treatment contribute to suppression of thermal deformationparticularly at a high temperature from a viewpoint of achieving bothimproved abrasion resistance and suppressed thermal deformation. Weassume the reason is as follows.

The high-temperature heat treatment is carried out at a temperature ashigh as the melting point+50° C. or more as described above. At thistemperature, crystal portions of liquid crystal polyester fiber melt tobe amorphous (liquid crystal) with orientation. Prior arts have aimed todisturb the orientation of the amorphous material by heat relaxation atsuch a high temperature.

It seems that the solid-phase polymerized liquid crystal polyester fiberhas a restriction point of which interaction is strong. Such arestriction point makes it difficult to sufficiently disturb theorientation of the amorphous material by heat relaxation only. If theheat-treatment temperature is increased to sufficiently disturb it, theheat relaxation is enhanced to disturb the orientation of the amorphousmaterial greatly, so that thermal deformation becomes great at a hightemperature. In other words, it is difficult only by adjustment of theheat-treatment temperature to achieve both the high abrasion resistanceand suppression of thermal deformation at a high temperature.

Therefore proper stretch is important. When the liquid polyester in anamorphous (liquid crystal) state oriented under high-temperature heattreatment is deformed slightly in a longitudinal fiber axial direction,the restriction point is destroyed while the orientation relaxation issuppressed by flow deformation. That effect reduces interaction betweenliquid crystal polyester to adjust the disturbance of orientation withina proper range to achieve both the high abrasion resistance andsuppression of thermal deformation.

According to our assumption described above, higher temperature andhigher stretch rate could be effective. However, the higher stretchcould contribute to destroying the restriction point greatly from 0% to3% of stretch while the effect would be saturated above the range. Onthe other hand, to make the stretch rate higher, it is necessary toreduce resistance against elongation deformation, namely elongationviscosity, while it is necessary to increase heat-treatment temperature.In such a case, thermal deformation cannot be suppressed since theeffect of the increased heat-treatment temperature surpasses the effectof stretch.

Our invention is characterized by an advantage that the improvement ofabrasion resistance of liquid crystal polyester fiber, which hasconventionally been controlled only by high-temperature heat-treatmenttemperature, can be controlled separately with interaction increase andorientation disturbance by a proper stretch. Such a characteristicachieve both the higher abrasion resistance and suppression of thermaldeformation.

The stretch rate should be 0.1% or more. The stretch rate of 0.1% ormore can achieve the improvement of abrasion resistance. To improve theabrasion resistance, it is preferable that the stretch rate is as highas 0.5% or more, preferably 0.6% or more. On the other hand, in casethat excessively high stretch rate might have too much disturbance oforientation of amorphous material to increase thermal deformation at ahigh temperature, it is preferable that the stretch rate is less than3.0%, preferably less than 2.5%.

It is preferable that the treatment velocity (yarn velocity) is 100m/min or more, preferably 200 m/min or more, further preferably 300m/min or more, so that the short-time processing can be achieved at ahigh temperature while the abrasion resistance and productivity areimproved although depending on treatment length. The upper limit ofprocessing velocity may be around 1,000 m/min from a viewpoint ofrunning stability of fiber.

It is preferable that the treatment length (heater length) is 100 mm ormore, preferably 500 mm or more, from a viewpoint of uniform processingin a case of non-contact heating although depending on heating method.It is preferable that it is 3,000 mm or less, preferably 2,000 mm orless, in case that too long treatment length might cause non-uniformprocessing and fiber meltdown by yarn sway inside a heater.

It is preferable that the fiber which has been heat treated at a hightemperature is taken up under a yarn route regulation with yarn routeguide in a range of 1 cm or more and 50 cm or less from the fiberheating region.

We found in a long-run evaluation that when a proper stretch isperformed to slightly extend the fiber in heat treatment, fluctuation ofstretch point might cause a longitudinal unevenness of fiber and yarnbreakage. We assume that the stretch point fluctuates because thetension is small enough to cause the yarn sway in the heat treatment ata temperature as high as the melting point+50° C. or more. If thestretch rate were 0%, the fiber wouldn't be extended at all and apossible yarn sway wouldn't cause the yarn breakage. It seems that thestretch causes the effect of yarn sway.

Therefore the regulation using the guide to reduce yarn sway iseffective. The liquid crystal polyester fiber before thehigh-temperature heat treatment can be fibrillated by scratch while theone after the heat treatment cannot be fibrillated by scratch at a lowtension since it already has an abrasion resistance enhanced.

It is preferable that the yarn route guide is provided in a positionrange of 1 cm or more and 50 cm or less from the heating region. Sincethe fiber is cooled (air-cooled) after exiting the heating region, itdeforms slightly as being cooled even after exiting the heating region.The effect of yarn sway is greatest in this region, and it is preferablethat the position range is 1 cm or more and 50 cm or less as a coolingregion, preferably 1 cm or more and 20 cm or less.

It is preferable that one or more guides are provided. It is preferablethat three or less guides are provided because too many guides mightincrease frequency of scratch to increase the possibility offibrillation. It is also preferable that a fiber is fed among aplurality of guides arranged in a fiber running direction. In this casethe position of provision means a position of guides closest to theheater.

The guide may be made of general material such as ceramic and metal. Toreduce damage to liquid crystal polyester fiber, it is preferable thatit has a metal surface plated with hard chrome. To keep a propercoefficient of friction not to damage fiber, it is preferable that thesurface roughness is 2 to 8, preferably 2 to 4 in terms of Rzjisdetermined by the method of JIS B0601:2001.

When the fiber contacts the guide, the running tension ratio before andafter the guide should not be too high to reduce damage to fiber. It ispreferable that a ratio of T2/T1 is 1.0 or more and 2.0 or less, wherethe running tension (T2) is a tension in a region closer to the windingside than the guide, and the running tension (T1) is a tension in aregion closer to the heating region.

In the last, a fiber structural change in high-temperature heattreatment will be explained from a viewpoint of difference in fibercharacteristics before and after processing.

Such a heat treatment means a short-time heat treatment at a hightemperature no less than the melting point (crystal-liquid crystaltransition temperature) of liquid polyester fiber, where thecrystallinity decreases but the orientation slightly relaxes. Such afact is shown in such a structural change that ΔHm1 decreases andhalf-value width at Tm1 increases while Δn doesn't change almost at allby the heat treatment. The processing time is too short to change themolecular weight. Reduced crystallinity generally causes a greatreduction of mechanical characteristics. Although the strength andelastic modulus decrease without increasing in our heat treatment, thestrength and elastic modulus are kept at a high level as maintaininghigh melting point (Tm1) and heat resistance to maintain the highmolecular weight and orientation. The peak temperature of tan δ becomeshigh by high-temperature heat treatment and the peak value rises. Thecrystallinity is decreased by the heat treatment, so that the peak valuerises and abrasion resistance improves. The peak temperature becomeshigh as a result that peaks of amorphous material are increased bycrystal melting. Namely, the abrasion resistance is low, because thepeak temperature is low and the crystallinity is high in a condition ofperforming no heat treatment at a high temperature.

EXAMPLES

Herein after, our invention will be explained with Examples. Eachcharacteristic value has been determined by the following method.

A. Heat Characteristics (Tm1, Tm2, Tm1 Peak Half-Value Width, ΔHm1,ΔHm2)

Differential calorimetry is carried out by DSC 2920 made by TAInstruments Corporation to determine temperature of endothermic peaktemperature Tm1 [° C.] under the condition of heating from 50° C. attemperature elevation rate of 20° C./min so that the heat of meltingΔHm1 [Jig] at Tm1 is determined. Maintaining temperature of Tm1+20° C.for five minutes after determination of Tm1, cooling is carried out downto 50° C. and then endothermic peak temperature Tm2 is determined underthe condition of heating again at temperature elevation rate of 20°C./min so that the heat of melting (ΔHm2) [J/g] at Tm2 is determined.Fibers and resins are subject to the same measurement. Thus determinedTm2 is regarded as a melting point for the measurement of resins.

B. Weight Average Molecular Weight in Terms of Polystyrene (MolecularWeight)

Using a mixed solvent of pentafluoro phenol/chloroform=35/65 (weightratio) as solvent, a sample for GPC measurement is prepared bydissolving to make the liquid crystal polyester have a concentration of0.04 to 0.08 weight/volume %. When insoluble substance remains evenafter leaving at room temperature for 24 hours, the sample is left foradditional 24 hours to collect the supernatant as a measurement sample.The sample is subject to a measurement using a GPC measurement apparatusmade by Waters Corporation to determine weight average molecular weight(Mw) in terms of polystyrene.

Column: Shodex K-806M; two pieces, K-802; one pieceDetector: Differential refractive index detector RI

Temperature: 23±2° C.

Flow rate: 0.8 mL/minInjection amount: 200 μL

C. Total Fineness, Single Fiber Fineness

A hank of fiber of 100 m is sampled with a sizing reel and then theweight [g] is multiplied at 1,000 times so that 3 times of measurementsare carried out per 1 level to calculate an average value as a fiberfineness [dtex]. The calculation result is divided by the filamentnumber to obtain a quotient as single fiber fineness [dtex].

D. Strength, Elongation, Elastic Modulus, Strength Fluctuation

Based on the method described in JIS L1013:2010 in condition of samplelength 100 mm and tensile velocity 50 mm/min, 10 times of measurementsper 1 level are carried out using Tensilon UCT-100 produced by OrientechCorporation to calculate an average value as strength [cN], elongation[%] and elastic modulus [cN/dtex]. Here, the elastic modulus means aninitial tensile resistance degree. The strength fluctuation iscalculated by the following formula using the greater absolute values ofdifference between the maximum or minimum value and the average value of10 times of strength measurements.

Strength fluctuation [%]={(|maximum or minimum value−averagevalue|/average value)×100}

E. Birefringence Index (Δn)

Using a polarization microscope (BH-2 made by Olympus Corporation), 5times of measurements are carried out per 1 level of sample by thecompensator method to calculate an average value.

F. Loss Tangent (tan δ)

The peak temperature and peak value of loss tangent (tan δ) aredetermined by measuring the dynamic viscoelasticity from 60° C. to 210°C. with VIBRON DDV-II-EP made by Orientec Corporation under condition offrequency 110 Hz, initial load 0.13 cN/dtex, temperature elevation rate3° C./m. When any peaks are not clearly observed, the maximum value oftan δ is regarded as a peak value and its temperature is regarded as apeak temperature in temperature elevation measurement. Namely, 60° C. or210° C. is a peak temperature when no peak is clearly observed. When aplurality of peaks are observed, the maximum value is regarded as a peakvalue. When the peak top value continues for a certain range oftemperature, the average value of the temperature is regarded as a peaktemperature.

G. Oil Adhesion Rate to Fiber Weight

A sample of 100 mg or more of fibers is dried at 60° C. for 10 min andits dry weight (W0) is measured. The fiber is immersed in 2.0 wt %sodium dodecyl benzene sulphonic acid solution containing water of whichweight is as 100 times or more as the fiber weight, and then subject toultrasonic cleaning at room temperature for 20 min. The cleaned fiber iswashed with water and dried at 60° C. for 10 min and its dry weight (W1)is measured. The oil adhesion rate is calculated by the followingformula.

(Adhesion rate [wt %])=(W0−W1)×100/W1

H. Abrasion Resistance C

Fiber applied with load of 1.23 cN/dtex is hung vertically. A ceramicrod guide (made by Yuasa Itomichi Kogyo Corporation, Material; YM-99C)having diameter of 4 mm is pushed onto the fiber at a contact angle of2.7° in a direction perpendicular to the fiber. The fiber is scratchedby the guide in a fiber axial direction at stroke length of 30 mm andstroke speed of 600 times/min and is observed with a stereo microscopeevery 30 sec. The time period, until white powder or fibril is observedon the rod guide or the fiber surface, is measured to determine theabrasion resistance C by averaging the 5 times of measurement resultsexcept for maximum and minimum values among 7 times of measurements.When neither the white power nor the fibril is observed after scratchingfor 360 sec, the time period is regarded as 360 sec.

I. Thermal Deformation at High Temperature (Dry-Heat Dimensional ChangeRate)

The dry-heat hank dimensional change rate determined according to themethod described in JIS L1013:2010 is regarded as a thermal deformationat high temperature. The measurement condition is such that load of 3.0cN/dtex is applied to measure a hank length while the treatment iscarried out at 150° C. for 5 min. The load is the same as the one to besubject to the dry-heat treatment. The thermal deformation is calculatedby the following formula.

(Thermal deformation rate [%])=(L1−L0)×100/L0

L0: hank length [cm] before dry-heat treatmentL1: hank length [cm] after dry-heat treatment

J. Yarn Breakage in Heat-Treatment Process

From the number of yarn-breakage times and the treated fiber length inthe heat-treatment process, the yarn-breakage times per 1,000,000 m iscalculated by the following formula. The treated fiber length is lengthcorresponding to one solid-phase polymerization package in Examples 1-8and Comparative Examples 1-6 while the length is 5,000,000 m in Examples9-11 and Reference Example 3.

(Yarn breakage [times/1,000,000 m]=(the number of yarn-breakage[times]×100/(treated fiber length [10,000 m])

L. Yarn-Making Property

The number of yarn-breakage times is measured when 500,000 m of fiber iswound in melt spinning process to determine the yarn-making propertyaccording to the following standard. Since the less the yarn breakage isthe better the yarn-making property is, it is industrially preferablethat the number of yarn breakage times is 2 or less.

● (Excellent): 0 times∘ (Good): 1-2 timesΔ (Acceptable): 3-4 timesx (Bad): 5 times or more

Reference Example 1

p-hydroxy benzoic acid of 870 parts by weight, 4,4′-dihydroxy biphenylof 327 parts by weight, hydroquinone of 89 parts by weight, terephthalicacid of 292 parts by weight, isophthalic acid of 157 parts by weight andacetic anhydride of 1,460 parts by weight (1.10 equivalent of the sum ofphenolic hydride group) were mixed in a reaction vessel of 5 L with anagitating blade and a distillation tube, and after temperature waselevated from room temperature to 145° C. by 30 min while agitated undernitrogen gas atmosphere, it was reacted at 145° C. for 2 hours.Thereafter, the temperature was elevated to 335° C. by 4 hours. Thepolymerization temperature was kept at 335° C., the pressure was reduceddown to 133 Pa for 1.5 hours, and further the reaction was continued for40 min, and at the time when the torque reached 28 kgcm, thecondensation polymerization was completed. Next, inside of the reactionvessel was pressurized at 0.1 MPa, the polymer was discharged asstrand-like material through a spinneret having one circular dischargeport having diameter of 10 mm, and it was pelletized by a cutter.Composition of thus obtained liquid crystal polyester, melting point andmolecular weight are shown in Table 1.

Reference Example 2

p-hydroxy benzoic acid of 907 parts by weight, 6-hydroxy-2-naphthoicacid of 457 parts by weight and acetic anhydride of 946 parts by weight(1.03 mol equivalent of the sum of phenolic hydride group) were mixed ina reaction vessel with an agitating blade and a distillation tube, andafter temperature was elevated from room temperature to 145° C. by 30min while agitated under nitrogen gas atmosphere, it was reacted at 145°C. for 2 hours. Thereafter, the temperature was elevated to 325° C. by 4hours. The polymerization temperature was kept at 325° C., the pressurewas reduced down to 133 Pa by 1.5 hours, and further the reaction wascontinued for 20 min, and at the time when the torque reached apredetermined level, the condensation polymerization was completed.Next, inside of the reaction vessel was pressurized at 0.1 MPa, thepolymer was discharged as strand-like material through a spinnerethaving one circular discharge port with diameter of 10 mm, and it waspelletized by a cutter. Composition of thus obtained liquid crystalpolyester, melting point and molecular weight are shown in Table 1.

TABLE 1 Reference Reference Example 1 Example 2 p-hydroxybenzoate unitmol % 54 73 4,4′-dihydroxy biphenyl unit mol % 16 0 Hydroquinone unitmol % 7 0 Terephthalic acid unit mol % 15 0 Isophthalic acid unit mol %8 0 6-hydroxy-2-naphthoic acid unit mol % 0 27 Liquid crystal Meltingpoint ° C. 320 283 polyester Weight average ×10,000 10.4 23.0 propertiesmolecular weight

Example 1

Using the liquid crystal polyester of Reference Example 1, after vacuumdrying was carried out at 160° C. for 12 hours, it was melt extruded bya single-screw extruder of φ15 mm made by Osaka Seiki KosakuCorporation, and the polymer was supplied to a spinning pack whilemetered by a gear pump. In the spinning pack, the polymer was filteredusing a metal nonwoven fabric filter, and the polymer was discharged inthe condition shown in Table 2. The introduction hole positioned rightabove the hole of the spinneret is straight shaped hole while theintroduction hole and the spinneret hole are connected with a taperedportion. The discharged polymer was cooled and solidified from the outerside of the yarn by an annular cooling air wind after passing throughthe heat retention region of 40 mm, and thereafter, a spinning oilsolution primarily constituting fatty acid ester compound was added, andall filaments were wound to the first godet roll at a spinning velocityshown in Table 2. After this was passed through the second godet roll atthe same velocity, all filaments except for one were sucked by a suctiongun, and the remaining one filament having the filament number 1 wastaken up into a pirn form via a dancer arm using a pirn winder (EFT typetake-up winder produced by Kamitsu Seisakusho Corporation, no contactroller contacting with a take-up package). During the take-up of 500,000m, yarn breakage didn't occur and the yarn-making property was good.Spun yarn properties are shown in Table 2. Besides, no peak was clearlyobserved while tan δ monotonically increased with temperature elevationin the measurement with raw yarn of spinning. Therefore, the peaktemperature defined in the specification was 210° C. and the peak valuewas 0.067.

TABLE 2 Example 1 Example 4 Example 5 Example 7 Example 8 Liquid crystalpolyester polymer Reference Reference Reference Reference ReferenceExample 1 Example 1 Example 1 Example 1 Example 2 Melt Spinningtemperature ° C. 345 345 345 345 325 spinning Discharge rate g/min 2.43.1 1.9 3.3 1.4 conditions Spinneret opening mm 0.13 0.13 0.13 0.13 0.20diameter Land length mm 0.26 0.26 0.26 0.26 0.30 L/D — 2.0 2.0 2.0 2.01.5 Opening number units 4 4 4 5 4 Yarn velocity m/min 1000 600 12001500 600 Yarn draft — 27 12 40 36 63 Spinnability — ●(Excellent)●(Excellent) ◯(Good) ◯(Good) ◯(Good) Spun yarn Weight average ×10,00010.2 10.2 10.2 10.0 8.8 properties molecular weight Total fineness dtex6.0 13.0 4.0 22.0 6.0 Filament number pieces 1 1 1 5 1 Single fiberfineness dtex 6.0 13.0 4.0 4.4 6.0 Tm1 ° C. 299 298 300 300 285 StrengthcN/dtex 6.4 6.1 6.2 6.6 8.7 Elongation % 1.5 1.5 1.4 1.4 2.1 Elasticmodulus cN/dtex 531 514 545 588 547

The fiber was rolled back from this spun fiber package by SSP-MV typerewinder (contact length of 200 mm, the number of winding of 8.7, taperangle of 45°) made by Kamitsu Seisakusho Corporation. The spun fiber wasunraveled in a vertical direction (direction perpendicular to thefiber-rounding direction). Without using a speed-regulating roller, oilsolution for solid-phase polymerization was supplied by an oiling rollerhaving a stainless-steel roll with satin-finished surface. The oilsolution for solid-phase polymerization employed was 6.0 wt % phosphatecompound (B) of phosphate compound (B1) shown in Chemical formula (4) inwhich 1.0 wt % inorganic particle (A) of talc SG-2000 (made by NIPPONTALC Co., Ltd.) was dispersed.

Kevlar felt (areal weight: 280 g/m2, thickness: 1.5 mm) rolled on astainless-steel bobbin with holes was used as a core member for theroll-back while the surface pressure was set to 100 gf. The oil adhesionrate to the rolled-back fiber of oil solution for solid-phasepolymerization as well as roll-back conditions are shown in Table 3.Next, the stainless-steel bobbin with holes was detached from therolled-back package, solid-phase polymerization was carried out in acondition of package where the fiber was taken up on the Kevlar felt.The solid-phase polymerization was carried out with a closed type ovento elevate temperature from room temperature to 240° C. by about 30 minand then keep the temperature at 240° C. for 3 hours. Again, thetemperature is elevated to the highest temperature shown in Table 3 by4° C./hour and kept the retention time shown in Table 3. In theatmosphere of oven, dehumidified nitrogen was supplied at a flow rate of20 NL/min and discharged from an exhaust port to prevent the innerpressure from becoming too high. Fiber properties after solid-phasepolymerization are shown in Table 3. The abrasion resistance was poorsince abrasion resistance C of fiber after solid-phase polymerizationwas 30 sec only.

TABLE 3 Example 1 Example 4 Example 5 Example 7 Example 8 Roll-backRoll-back velocity m/min 400 400 400 400 400 condition Winding tensioncN/dtex 0.16 0.10 0.30 0.10 0.16 Winding density g/cc 0.5 0.3 0.6 0.30.5 Winding quantity ×10,000 [m] 50.0 25.0 10.0 10.0 10.0 Oil adhesionrate (a + b) of oil wt % 15.0 12.2 18.6 20.0 15.2 solution forsolid-phase polymerization Solid-phase Highest temperature ° C. 290 290290 290 290 polymerization Retention time to reach hr 20 20 20 20 20highest temperature Fiber properties Weight average molecular weight×10,000 39.6 38.2 41.2 40.8 37.0 after solid-phase Total fineness dtex 714 4 24 6 polymerization Filament number pieces 1 1 1 5 1 Single fiberfineness dtex 6.5 13.9 4.3 4.8 6.5 Strength cN/dtex 22.6 20.1 21.7 21.321.1 Elongation % 2.8 2.6 2.6 2.6 3.1 Elastic modulus cN/dtex 988 9521072 1014 820 Tm1 ° C. 332 332 334 333 318 ΔHm1 J/g 9.0 8.6 10.2 9.211.4 Peak half-value width at Tm1 ° C. 10 12 8 10 7 Tm2 ° C. 333 332 334331 316 ΔHm2 J/g 1.2 1.2 1.1 1.1 0.9 Oil adhesion per fiber weight wt %7.8 7.0 8.2 9.0 7.5

Finally, fiber was unraveled from the package after solid-phasepolymerization and successively subject to a high-temperaturenon-contact heat treatment. The package after solid-phase polymerizationwas attached to a free roll creel (having a shaft and bearings to freelyrotate outer layer, without brakes and drive sources) and therefrom theyarn was drawn out in a lateral direction (fiber-rounding direction).Successively the fiber was dipped in a bath (with no guides to contactfiber inside) of bath length of 150 cm (contact length of 150 cm)provided with slits at both ends to remove oil solution by washing. Thewashing liquid containing 0.2 wt % nonionic-anionic surfactant (Gran UpUS-30 made by Sanyo Chemical Industries Corporation) controlled at 50°C. with an external tank was supplied into a tank by a pump. The liquidwas supplied into the tank through a pipe having holes provided atintervals of 5 cm in the tank to generate a liquid flow through the pipein the tank. The washing liquid overflowed from slits and holes foradjusting liquid level was returned to the external tank in a certainmechanism.

Successively the fiber was dipped in a bath (with no guides to contactfiber inside) of bath length of 23 cm (contact length of 23 cm) providedwith slits at both ends to be rinsed with water at 50° C. The washedfiber was passed through a bearing roller guide and was contacted to airflow to blow off the water to be removed, and then was passed throughthe first roller having a separate roller at 200 m/min. The creel is afree roll, to which tension is applied to unravel the solid-phasepolymerized package to feed the fiber.

The fiber which had passed through the roller was fed between heatedslit heaters and was subject to high-temperature heat treatment underthe conditions shown in Table 4. The slit heaters were not provided withguides inside while the heater didn't contact the fiber. The fiber whichhad passed through the heater was passed through the second rollerhaving a separate roller. The yarn velocity before heat treatmentrepresents a surface velocity of the first roller while the yarnvelocity after heat treatment represents a surface velocity of thesecond roller. A finishing oil solution primarily consisting of fattyacid polyester compound is added to the fiber which had passed throughthe second roller as using an oiling roller made of ceramic, and wastaken up into a pirn form with EFT type bobbin traverse winder (made byKamitsu Seisakusho Corporation). Fiber properties after high-temperatureheat treatment are shown in Table 4. An of the liquid crystal polyesterfiber was 0.35 representing a high orientation.

Because the fiber obtained in Example 1 achieved both high abrasionresistance and low thermal deformation rate, it is expected thatprocessability could be improved at a higher processing, faults could bereduced and thermal deformation could be suppressed in processing at ahigh temperature.

TABLE 4 Compar- Compar- Compar- Compar- ative ative ative ative Example1 Example 1 Example 2 Example 3 Example 2 Example 3 Example 4 Example 4Fiber after solid-phase polymerization Example 1 Example 1 Example 1Example 1 Example 1 Example 1 Example 1 Example 4 High-temperatureHeater temperature ° C. 480 480 480 510 480 480 480 500 heat treatmentHeater length mm 1000 1000 1000 1000 1000 1000 1000 1000 Yarn velocitybefore m/min 198 200 190 190 199 195 193 198 heat-treatment Yarnvelocity after m/min 200 200 200 200 200 200 200 200 heat-treatmentStretch rate % 1.0 0.0 5.0 5.0 0.5 2.5 3.5 1.0 Treatment time sec 0.300.30 0.30 0.30 0.30 0.30 0.30 0.30 Running tension gf 0.5 0.3 1.8 0.30.4 0.9 1.2 0.5 Running stress cN/dtex 0.08 0.05 0.30 0.05 0.06 0.140.20 0.08 Yarn breakage times/ 0 12 50 16 0 10 20 0 million meters Fiberproperties Weight average ×10,000 39.3 39.2 Sampling 39.2 39.3 39.2 39.238.0 after high- molecular weight impossible temperature Total finenessdtex 6.0 6.0 6.0 6.0 6.0 6.0 12.9 heat treatment Filament number pieces1 1 1 1 1 1 1 Single fiber fineness dtex 6.0 6.0 6.0 6.1 6.1 6.1 12.9Strength cN/dtex 18.8 17.9 17.8 18.4 19.2 19.3 17.1 Elongation % 2.9 2.93.0 2.9 2.8 2.8 2.8 Elastic modulus cN/dtex 785 745 738 761 832 851 709Tm1 ° C. 323 322 322 323 323 320 322 ΔHm1 J/g 0.8 0.6 0.6 0.7 1.5 5.10.6 Peak half-value ° C. 25 31 35 28 21 15 33 width at Tm1 Tm2 ° C. 333333 334 333 333 333 333 ΔHm2 J/g 1.1 1.0 1.0 1.1 1.1 1.2 1.1 Abrasionresistance sec 360 360 360 360 180 48 240 tan δ peak value — 0.077 0.0910.092 0.085 0.065 0.059 0.072 tan δ peak temperature ° C. 143 145 145144 142 139 143 Oil adhesion per fiber wt % 0.8 0.8 0.8 0.8 0.8 0.8 0.6weight Thermal deformation % 0.4 1.1 1.2 0.7 0.3 0.2 0.5 rate at hightemperature Compar- Compar- ative ative Example 5 Example 6 Example 7Example 8 Example 5 Example 6 Fiber after solid-phase polymerizationExample 5 Example 1 Example 7 Example 8 Example 1 Example 8High-temperature Heater temperature ° C. 460 500 520 480 No heat- Noheat- heat treatment Heater length mm 1000 1000 1000 1000 treatmenttreatment Yarn velocity before m/min 198 396 199 198 carried out carriedout heat-treatment Yarn velocity after m/min 200 400 200 200heat-treatment Stretch rate % 1.0 1.0 0.5 1.0 Treatment time sec 0.300.15 0.13 0.30 Running tension gf 0.4 0.7 0.8 0.5 Running stress cN/dtex0.03 0.11 0.08 0.08 Yarn breakage times/ 10 0 10 10 million meters Fiberproperties Weight average ×10,000 40.8 39.2 40.1 37.1 39.6 36.9 afterhigh- molecular weight temperature Total fineness dtex 4.0 6.0 21.8 6.86.0 6.0 heat treatment Filament number pieces 1 1 5 1 1 1 Single fiberfineness dtex 4.0 6.0 4.4 6.8 6.0 6.0 Strength cN/dtex 18.0 18.6 16.318.5 21.1 20.1 Elongation % 2.8 2.9 2.6 3.0 2.7 3.0 Elastic moduluscN/dtex 765 764 704 749 905 767 Tm1 ° C. 322 322 323 306 332 318 ΔHm1J/g 0.7 0.8 0.7 5.8 9.0 11.4 Peak half-value ° C. 26 26 27 16 10 7 widthat Tm1 Tm2 ° C. 334 333 332 318 333 316 ΔHm2 J/g 0.9 1.2 1.1 0.9 1.2 0.9Abrasion resistance sec 120 240 240 60 30 30 tan δ peak value — 0.0770.075 0.080 0.085 0.041 0.064 tan δ peak temperature ° C. 144 144 145110 120 65 Oil adhesion per fiber wt % 1.0 1.0 1.6 0.9 0.9 0.9 weightThermal deformation % 0.6 0.5 0.8 0.3 0.1 0.1 rate at high temperature

Comparative Examples 1-4, Examples 2 and 3

The effect of stretch rate in a high-temperature heat treatment wasevaluated. The solid-phase polymerized yarn obtained in Example 1 washeat treated at a high temperature by the same method as Example 1except that the heat-treatment temperature and stretch rate were changedaccording to Table 4. The stretch rate was 5.0% in Comparative Example2, in which the yarn breakage occurred right after the heat treatment.The yarn breakage occurred twice during the treatment of 40,000 m tocancel the test because a sample of 30,000 m or more was not obtained.Properties of obtained fiber are shown in Table 4. The table shows thatobtained fiber can achieve both excellent abrasion resistance and lowthermal deformation rate with less yarn breakage when the stretch rateis 0.1% or more and less than 3.0%. The stretch rate was low inComparative Example 1, in which relatively many times of yarn breakageoccurred in heat treatment while the tan δ peak value and thermaldeformation rate were high. The stretch rate was 5.0% in ComparativeExample 3, in which the tan δ peak value increased and thermaldeformation rate was high because the temperature was increased tosuppress yarn breakage. The stretch rate was high in Comparative Example4, in which the abrasion resistance was poor in spite of low tan δ peakvalue.

Examples 4 and 5

The effect of single fiber fineness was evaluated. The melt spinning wascarried out by the same method as Example 1 except that the dischargerate and spinning velocity were changed according to Table 2. The singlefiber fineness was small in Example 5, in which the yarn breakageoccurred once although spinnability was good. Properties of obtainedfiber are shown in Table 2. Next, the solid-phase polymerization wascarried out by the same roll-back method as Example 1, except that thewinding condition (quantity, tension and density) were changed accordingto Table 3. Properties of obtained fiber after solid-phasepolymerization are shown in Table 3. The high-temperature heat treatmentwas carried out by the same method as Example 1, except that theheat-treatment temperature was changed according to Table 4. The singlefiber fineness was small in Example 5, in which the yarn breakageoccurred once during the treatment of 100,000 m although processabilityhad almost no problem. Properties of obtained fiber are shown in Table4. The table shows that obtained fiber can achieve both excellentabrasion resistance and low thermal deformation rate even under varioussingle fiber fineness when the stretch rate is 0.1% or more and lessthan 3.0% under controlled heat-treatment temperature.

Example 6

The effect of heat-treatment velocity was evaluated. The solid-phasepolymerized yarn obtained in Example 1 was heat treated at a hightemperature by the same method as Example 1, except that theheat-treatment temperature and stretch rate were changed according toTable 4. Properties of obtained fiber are shown in Table 4. The tableshows that obtained fiber can achieve both excellent abrasion resistanceand low thermal deformation rate with less yarn breakage even undervarious velocities of treatment when the stretch rate is 0.1% or moreand less than 3.0% under controlled heat-treatment temperature.

Example 7

The effect of the number of filaments was evaluated. The melt spinningwas carried out by the same method as Example 1, except that thedischarge rate, spinneret opening number and spinning velocity werechanged according to Table 2 while discharged filaments were convergedto make a multifilament. The yarn breakage occurred once althoughspinnability had no problem. Properties of obtained fiber are shown inTable 2. Next, the solid-phase polymerization was carried out by thesame roll-back method as Example 1 except that the winding quantity waschanged according to Table 3. Properties of obtained fiber aftersolid-phase polymerization are shown in Table 3. The high-temperatureheat treatment was carried out by the same method as Example 1, exceptthat the heat-treatment temperature and stretch rate were changedaccording to Table 4. The yarn breakage occurred once during thetreatment of 100,000 m although processability had almost no problem.Properties of obtained fiber are shown in Table 4. The table shows thatobtained fiber can achieve both excellent abrasion resistance and lowthermal deformation rate even with multifilament when the stretch rateis 0.1% or more and less than 3.0% under controlled heat-treatmenttemperature.

Example 8

The effect of polymer composition was evaluated. The polymer obtained inReference Example 2 was melt spun by the same method as Example 1,except that the spinneret opening number, land length, discharge rateand spinning velocity were changed according to Table 2. The yarnbreakage occurred once although spinnability had no problem. Propertiesof obtained fiber are shown in Table 2. Next, the solid-phasepolymerization was carried out by the same roll-back method as Example1, except that the winding quantity was changed according to Table 3.Properties of obtained fiber after solid-phase polymerization are shownin Table 3. Next, the high-temperature heat treatment was carried out bythe same method as Example 1. The yarn breakage occurred once during thetreatment of 100,000 m although processability had almost no problem.Properties of obtained fiber are shown in Table 4. The table shows thatobtained fiber can achieve both good abrasion resistance and low thermaldeformation rate even under various composition when the stretch rate is0.1% or more and less than 3.0% under controlled heat-treatmenttemperature.

Comparative Examples 5 and 6

The effect of high-temperature heat treatment was evaluated. Using thesolid-phase polymerized yarn obtained in Examples 1 and 8, the fiber wasfed and taken up by the same heat-treatment method as Examples 1 and 8,except that the rollers before and after the heater were run at 200m/min at room temperature while the heater was not operated. Namely, thesolid-phase polymerized fiber was unraveled and washed to be rolled backwithout heat treatment. Properties of obtained fiber are shown in Table4. The table shows that the high-temperature heat treatment was notcarried out to make the abrasion resistance low although thermaldeformation rate was low. The table also shows that both good abrasionresistance and low thermal deformation rate cannot be achieved in a casesuch as Comparative Example 5 in which the tan δ peak value was low andComparative Example 6 in which the peak temperature was low.

Example 9, Reference Example 3

The effect of providing a guide at the exit of heating region wasdetermined through a long-run evaluation. Namely, the solid-phasepolymerized yarn of 5,000,000 m was subject to high-temperature heattreatment to evaluate the yarn breakage in particular. Using thesolid-phase polymerized yarn obtained in Example 1, the high-temperatureheat treatment was carried out by the same method as Example 1, exceptthat two pieces of hard chrome-plated satin-finished metal rod guides(made by Yuasa Itomichi Kogyo Corporation, Rzjis=2-4) having diameter of3.8 mm were provided at the exit of heater for heat treatment accordingto Table 5. The treatment length was 5,000,000 m corresponding to 10pieces of solid-phase polymerized yarn (Example 9). The high-temperatureheat treatment of 5,000,000 m was carried out under the same conditionas Example 1 without providing a guide (Reference Example 3). Referenceexample 3 and Example 1 have a difference of treatment length only.Properties of obtained fiber are shown in Table 5. The table shows thatExample 9 is excellent in running stability with less yarn breakagerelative to Reference Example 3. The properties show small strengthfluctuation rates representing less fluctuation. We presume the stabletreatment contributed to a smaller variation in the example because thestrength, elongation and elastic modulus were slightly higher thanReference Example 3. Thus provided guide at the exit of heating regioncan regulate the yarn route to suppress yarn breakage.

TABLE 5 Reference Example 9 Example 3 Example 10 Example 11 Fiber aftersolid-phase polymerization Example 1 Example 1 Example 1 Example 1High-temperature Heater temperature ° C. 480 480 480 480 heat treatmentHeater length mm 1000 1000 1000 1000 Yarn velocity before m/min 198 198195 195 heat treatment Yarn velocity after m/min 200 200 200 200 heattreatment Stretch rate % 1.0 1.0 2.5 2.5 Treatment time sec 0.30 0.300.30 0.30 Guide setting position cm 5 No guide 3 50 Running tension atgf 0.4 — Unmeasurable 0.9 heating region side (T1) Running tension at gf0.5 0.5 0.9 0.9 rewind side (T2) T2/T1 — 1.25 — — 1.00 Yarn breakagecaused by times/ 0.2 0.8 2.2 8.0 heat treatment of million 5,000,000 mmeters Fiber properties after Weight average ×10,000 39.3 39.3 39.2 39.2high-temperature molecular weight heat treatment Total fineness dtex 6.06.0 6.0 6.0 Filament number pieces 1 1 1 1 Single fiber fineness dtex6.0 6.0 6.1 6.1 Strength cN/dtex 18.9 18.6 19.3 19.1 Strength variationrate % 4 8 5 5 Elongation % 2.9 2.8 2.9 2.8 Elastic modulus cN/dtex 788776 851 816 Tm1 ° C. 322 323 324 323 ΔHm1 J/g 0.7 0.8 1.5 1.5 Peakhalf-value width ° C. 26 25 22 21 at Tm1 Tm2 ° C. 332 333 333 333 ΔHm2J/g 1.1 1.1 1.1 1.1 Abrasion resistance sec 360 360 198 180 tan δ peakvalue — 0.078 0.077 0.067 0.065 tan δ peak temperature ° C. 144 143 143142 Oil adhesion per wt % 0.8 0.8 0.8 0.8 fiber weight Thermaldeformation % 0.4 0.4 0.3 0.3 rate at high temperature

Examples 10 and 11

The effect of position for setting a guide at the exit of heating regionwas determined through a long-run evaluation. The high-temperature heattreatment was carried out by the same method as Example 9, except thatthe guide setting position was changed according to Table 5. Examples 10and 11 have the same stretch rate as Example 3, and have different guidesetting positions and treatment lengths from Example 3. Properties ofobtained fiber are shown in Table 5. T1 wasn't able to be measured sincethe guide setting position was close to the heating region (heater) inExample 10. The yarn breakage was reduced in Example 10 better thanExample 3 in spite of long treatment length. The number of yarn breakagetimes was reduced even in Example 11 better than Example 3. Thus theposition distant from the heating region by 1 cm or more and 50 cm orless can suppress yarn breakage.

1. A method of producing a melt-spun liquid crystal polyester fiber,said method comprising: melt spinning a liquid crystal polyester fiberthereby polymerizing said fiber in a solid phase; and heat stretchingthe polymer at a temperature of an endothermic peak (Tm1)+50° C. or moreand at a stretch rate of 0.1% or more and less than 3.0%, wherein theendothermic peak is observed by a differential calorimetry under atemperature elevation condition of 20° C./min from 50° C.; whereinmelt-spun liquid crystal polyester has: a peak half-value width of 15°C. or more at an endothermic peak (Tm1) observed by a differentialcalorimetry under a temperature elevation condition of 20° C./min from50° C.; a weight-average molecular weight in terms of polystyrene of250,000 or more and 2,000,000 or less; a peak temperature of a losstangent (tan δ) of 100° C. or more and 200° C. or less; and a peak valueof the loss tangent (tan δ) of 0.060 or more and 0.078 or less; andwherein the peak temperature and peak value of loss tangent (tan δ) aredetermined by measuring a dynamic viscoelasticity from 60° C. to 210° C.under the conditions of a frequency of 110 Hz, an initial load of 0.13cN/dtex, and a temperature elevation rate of 3° C./m.
 2. The methodaccording to claim 1, wherein the heated fiber is taken up under a yarnroute regulation with yarn route guide in a range of 1 cm or more and 50cm or less from an exit portion of a heating region.
 3. The methodaccording to claim 1, wherein the liquid crystal polyester is a) apolymer of an aromatic oxycarboxylic acid component; b) a polymer of anaromatic dicarboxylic acid component, an aromatic diol component and/oran aliphatic diol component; or c) a copolymer of a) and b).